1. Field of the Invention
The present invention relates to a device and a method for controlling tape travelling speed and a medium for recording its control program that detect the rotational state of a tape reel for making a magnetic tape travel and control the travelling speed of the magnetic tape in response to the detected rotational state of the tape reel.
2. Description of the Related Art
Conventional tape travelling speed control devices are disclosed in Japanese Unexamined Patent Prepublications H4-103059 and S59-107444, in which, to shorten the time necessary for fast-feeding and rewinding of the tape, the former performs the judgement in the vicinity of a leader and a trailer of a magnetic tape so as to reduce the tape travelling speed at the leader and the trailer of the magnetic tape while enhancing the entire tape travelling speed; the latter controls the tape travelling speed step by step.
The conventional tape travelling speed control devices, however, detect the tape travelling speed in controlling the travelling speed of the magnetic tape without taking a detection error caused by slackening of the magnetic tape or the like into account.
Accordingly, when the magnetic tape is in such abnormal travelling state as being slackened, until the slackening of the magnetic tape is resolved and the magnetic tape returns to the normal travelling state, the accurate tape travelling speed cannot be detected. This causes an erroneous speed control that causes the tape reel to rotate up to the leader or the trailer of the magnetic tape while keeping elevated rotational speed. This applies an excessive load to the magnetic tape in the state that the magnetic tape is stretched at the leader or the trailer, damaging the magnetic tape to destroy its durability.
The present invention has been made in view of the above situation and it is an object of the invention to provide a tape travelling speed control device which can reduce damages on a magnetic tape by preventing an excessive load from being applied to the magnetic tape when the magnetic tape is not in the normal travelling state.
A tape travelling speed control device provided by the present invention is equipped with a supply reel pedestal to drive a supply reel and a winding reel pedestal to drive a winding reel, both used for a videotape, and having:
rotation detection elements for outputting reel pulses when the supply reel pedestal and the winding reel pedestal are rotated at a predetermined angle respectively,
RAM for storing a ratio of intervals of the reel pulses outputted by the respective rotation detection elements, and
a CPU for controlling the tape travelling speed by calculating the ratio between the intervals, controlling to store the ratio to the RAM, comparing the ratio detected before the tape is stopped with the ratio after the tape is traveled, and determining that the ratio is correct when an error of the ratios is smaller than a threshold.
That is, a tape travelling speed control device is designed to have:
a reel rotational state detection unit for detecting a rotational state of a tape reel for making a magnetic tape travel,
a reel rotational state storing unit for storing a rotational state of the tape reel detected by said reel rotational state detection unit at appropriate times, and
a tape travelling speed control unit for comparing the stored rotational state with the latest rotational state and controlling the travelling speed of said magnetic tape in accordance with whether the rotational state falls within a normal range based on a difference between the stored rotational state and a current rotational state
In the present invention having the constitution, the reel rotational state detection unit detects the rotational state of the tape reel for making the magnetic tape travel and the tape travelling speed control unit compares the rotational state of the tape reel which is detected by the reel rotational state detection unit at appropriate times and is stored by the reel rotational state storing unit with the latest rotational state. Then, the tape travelling speed control unit controls the travelling speed of the magnetic tape on the basis of whether the comparison result of the rotational state falls in a normal range or not based on a difference between the moments in the stored rotational state and a current rotational state.
As explained above, the present invention can provide the tape travelling speed control device which can reduce the damages on the magnetic tape by preventing an excessive load being applied to the magnetic tape when the magnetic tape is not in the normal travelling state.
As an example of the rotational state detected at appropriate time stated here, the reel rotational state storing unit is constituted to store the rotational state of the tape reel which is detected by the reel rotational state detection unit immediately before the magnetic tape has previously stopped.
In the constitution, the rotational state of the tape reel detected immediately before the magnetic tape has previously stopped is compared with the latest rotational state.
That is, immediately before the magnetic tape has previously stopped, the magnetic tape is usually travelling in the normal state so that there is no possibility that the magnetic tape is slackened whereby the reel rotational state detection unit detects the normal rotational state.
On the other hand, making the stopped magnetic tape travel again, since a tape reel, when stopped, tends to rotate excessively due to the inertial force, causes the magnetic tape to be frequently slackened, preventing normal rotational state from being detected until the slackening of the magnetic tape is resolved.
Accordingly, when the rotational state detected immediately before the stop and the latest rotational state are compared, if the difference between the rotational states does not fall within a predetermined range, it is judged that the normal rotational state cannot be detected since the slackening of the magnetic tape remains; If within the predetermined range, judged that the slackening of the magnetic tape is resolved, namely the normal rotational state is detected.
Due to the constitution, when the magnetic tape is made to travel again after the stop, the execution of the unintentional speed control can be prevented.
In this manner, as the rotational state detected at appropriate times, storing the rotational state detected immediately before the stop of the previous rotational state and using the rotational state for comparison, even when the slackened magnetic tape is started rotating, detection based on the rotational state in the normal travelling immediately before the stop usefully prevents the unintentional speed control. However, this merely constitutes one example.
A case in which the tape travelling speed of the magnetic tape is controlled based on the result of comparison with the rotational state stored in the normal travelling is not limited to the case in which the magnetic tape is made to travel again after the magnetic tape is stopped. For example, the case may include a case in which when the tape travelling speed control unit executes an abnormal control, the control is executed by comparing with the normal rotational state immediately before the execution of the abnormal control or a case in which when the deflection is generated on the travelling magnetic tape, the control may be executed based on the comparison with the normal rotational state immediately before the generation of the deflection.
Further, the appropriate time is not limited to the case in which the magnetic tape travels in the normal state but includes a case in which the magnetic tape is not in the normal travelling state. For example, in the case that the rotational state detected when the magnetic tape is slackened is stored and then the latest rotational state is detected when the slackening of the magnetic tape is resolved, the difference between the rotational states does not fall within a predetermined range. Here, however, by updating and storing the latest rotational state, the difference falls in the predetermined range in the next comparison. Accordingly, it is confirmed that the normal rotational state is detected and it becomes possible to execute the travelling speed control of the magnetic tape in the usual time.
This prevents the unintentional control in which the tape reel is rotated exceeding the desired rotational speed caused by the travelling speed control of the magnetic tape as usual when it is not confirmed whether the normal rotational state is detected or not, and thereby preventing the magnetic tape from being applied with an excessive load.
Although the reel rotational state storing unit may be constituted so as to store the rotational state as the comparison object, only at predetermined times such as the time immediately before the stop, as mentioned above, and it may also be constituted to store the latest rotational state while sequentially updating the latest rotational state.
As an example of the rotational state described above, the reel rotational state detection unit detects the ratio of rotation between the feeding reel to deliver the magnetic tape and the winding reel to wind the delivered magnetic tape;
the reel rotational state storing unit stores the ratio of rotation detected by the reel rotational state detection unit at appropriate times; and
the tape travelling speed control unit compares the ratio of rotation stored in the reel rotational state storing unit with the latest ratio of rotation, and controls the travelling speed of the magnetic tape on the basis of whether a comparison result falls within a normal range based on the difference between the stored rotational state and a current rotational state.
Due to the constitution, the reel rotational state detection unit detects the ratio of rotation between the feeding reel and the winding reel as the rotational state of the tape reel.
Here, the tape travelling speed control unit compares the ratio of rotation stored in the reel rotational state storing unit with the latest ratio of rotation and controls the travelling speed of the magnetic tape on the basis of whether the difference is within the normal range or not based on the difference between the moments in the stored rotational state and a current rotational state.
Due to the constitution, the rotational states of the feeding reel and the winding reel can be compared by succinctly expressing them with a single parameter.
In this manner, the execution of the speed control based on the ratio of rotation between the feeding reel and the winding reel as the tape reels is advantageous since both rotational states of the feeding reel and the winding reel can be succinctly expressed with the single parameter. Such constitution, however, constitutes only one example.
Accordingly, from a viewpoint that it is sufficient for the present invention that the rotational speed of the magnetic tape can be controlled based on the rotational state of the tape reel, it may be possible to treat the rotational speed of the feeding reel and the rotational speed of the winding reel separately. Further, it may be also possible to use the interval of the reel pulses which are synchronous with the rotation of the tape reel as the rotational state.
As a constitutional example of the tape travelling speed control unit, the tape travelling speed control unit sets the acceleration target of the magnetic tape at the time of fast-feeding or rewinding the magnetic tape and compares the rotational state stored by the reel rotational state storing unit and the latest rotational state, and accelerates the magnetic tape up to the set acceleration target only when the difference of the rotational state falls in the normal range based on the difference between the moments in the stored rotational state and a current rotational state.
With the constitution, the tape travelling speed control unit sets the acceleration target of the magnetic tape when the magnetic tape is fast-fed or rewound.
Then, the rotational state stored by the reel rotational state storing unit and the latest rotational state are compared with each other and the magnetic tape is accelerated up to the set acceleration target only when the difference of the rotational state falls in the normal range based on the difference between the moments in the stored rotational state and a current rotational state.
That is, when the tape reel is accelerated to the speed set as the acceleration target in a usual manner without confirming whether the normal rotational state is detected or not, there is a possibility that the tape reel is accelerated exceeding the desired rotational speed and an excessive load is applied to the magnetic tape.
Accordingly, when the difference of the rotational state does not fall in the normal range based on the difference between the moments in the stored rotational state and a current rotational state, the magnetic tape based on the set acceleration target is not accelerated such that the magnetic tape is made to travel at a constant speed without executing the acceleration or the like.
Due to the constitution, at the time of performing the fast-feeding or the rewinding, the tape reel is prevented from being accelerated and hence, the magnetic tape is prevented from being applied with an excessive load.